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参数资料
| 型号： | AT76C651 |
| 厂商： | ATMEL CORP |
| 元件分类： | 消费家电 |
| 英文描述： | Digital Reception/Transmission Integrated DVB compliant QAM Demodulator(兼容DVB的正交振幅调制解调电路) |
| 中文描述： | SPECIALTY CONSUMER CIRCUIT, PQFP100 |
| 封装： | TQFP-100 |
| 文件页数： | 27/37页 |
| 文件大小： | 497K |
| 代理商： | AT76C651 |
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AT76C651
27
CARCONST: 0x39/0x3A/0x3B (read)
b7
b6
The constellation points after gain adjustment, timing
recovery, equalization and carrier recovery can be col-
lected without breaking down the demodulation and the
channel decoding. The two components (I, Q), with 12-bit
precision, are collected in three bytes:
Byte 1 (0x39): 8 MSB of I
Byte 2 (0x3A): 8 MSB of Q
Byte 3 (0x3B): The 4 MSB of byte 3 are equal to the 4
LSB of I and the 4 LSB of byte 3 are equal to the 4 LSB
of Q.
Byte 1 should be collected first. When the address of this
byte is detected by the AT76C651, then a constellation
point (I: 12 bits, Q: 12 bits) is memorized and only the 8
MSBs of I are sent as data on the I
2
C bus. Byte 2 and byte
3 can be collected later; their content does not change
unless byte 1 is collected again.
AGC2
AGC2CFG: 0x42 (read/write)
b7
Two operating modes exist for agc2: boost mode and nor-
mal mode. After a reset or a soft clear, the agc2 is in boost
mode and unlocked. During this phase, equalizer and car-
rier are inhibited. The switch from boost mode to normal
mode happens when agc2 locks. The agc2 loop bandwidth
can be controlled through loopbw2 during boost mode and
by loopbw1 during normal mode. In both cases the loop
bandwidth is proportional to loopbw.
Table 15 gives the value of AGC2CFG for the different
QAM in automatic configuration.
AGC2INIT: 0x43 and 0x44 (read/write)
These registers configure the initial agc2 gain.
b7
b6
b5
AGC2INIT is coded in a floating format with a mantissa
coded with 11 unsigned bits and an exponent coded with 5
signed bits, defined as follows:
Exponent must be in the range -6 to 13, and mantissa
takes its value in the range 1024 to 2047.
Equalizer
EQUCFG: 0x51 (read/write)
This register controls the equalizer operating mode.
b7
b6
b5
inh: When set to 1, this parameter inhibits the equalizer;
all equalizer taps are set to 0 except central tap, which is
equal to 1 (in complex format). In standard configuration
it is set to 0.
fre: When set to 1 it freezes the equalizer taps
adaptation. The equalizer behaves as a complex FIR
(finite impulse response). In standard configuration it is
set to 0.
len: The equalizer has 32 taps when this parameter is
set to 1 and only 16 taps when set to 0. The first mode
can be selected only if the ratio between f
ref
and f
symbol
is
higher or equal to 8(f
ref
/f
symbol
≥
8). In standard
configuration it is set to 1.
I (11:4)
0x39
Q (11:4)
0x3A
I (3:0)
Q (3:0)
0x3B
b5
b4
b3
b2
b1
b0
res
0x42
b6
b5
b4
b3
b2
b1
b0
loopbw2
loopbw1
Table 15.
QAM
AGC2CFG
QPSK
0x34
QAM-16
0x35
QAM-32
0x35
QAM-64
0x34
QAM-128
0x33
QAM-256
0x32
QAM-512
0x31
QAM-1024
0x30
0x43
mantissa (2:0)
0x44
b4
b3
b2
b1
b0
exponent (4:0)
mantissa (10:3)
exponent
floor
2
log
agc
2
gain
(
))
(
=
mantissa
floor agc
2
gain
2
exponent
–
×
1024
×
)
=
inh
fre
len
structure
0x51
b4
b3
b2
b1
b0
step
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